It is known that creating a vortex in a container is an effective means for mixing its contents. Common laboratory vortexers use a support cup or a resilient container receiving surface mounted eccentrically on a motor in order to translate the lower end of a container in a circular path or orbit at a high speed and thereby create an effective vortex in the fluid held by the container. Exemplary of this type of device are those disclosed in U.S. Pat. Nos. 4,555,183 (Thomas) and 3,850,580 (Moore et al.). These devices are manual in that an operator is required to hold the vessel in contact with the eccentrically movable means to create the vortex in the fluid disposed in the container.
Thomas discloses the use of an eccentrically rotating cylinder having a cup to receive the lower portion of a laboratory test tube in a V-shaped depression. The tube can only be removed or inserted into the cup by lifting or lowering the tube.
Such vortex type device would be extremely advantageous in an automated chemical analysis instrument as it is not invasive and therefore avoids the concern of contamination associated with an improperly cleaned invasive mixing means. A device the incorporates this type of mixing into an automated testing apparatus is disclosed in an article by Wada et al. entitled "Automatic DNA Sequencer: Computer Program MIcro Chemical Manipulator for the Maxim-Gilbert Sequencing Method," Review of Scientific Instruments 54 (11), Nov. 1983, pages 1569-1572. In the device disclosed in this article, a plurality of reaction vessels are held flexibly in a centrifuge rotor. A rotational vibrator is mounted on a vertically moving cylinder. When mixing is desired the reaction vessel is positioned in a mixing station directly above the rotational vibrator. The vertically moving cylinder is moved upwardly to contact the bottom of the reaction vessel with the rotary vibrating rubber portion of the rotational vibrator. The vibrating rubber portion is V-shaped in cross-section to engage a test tube having a V-shaped bottom. The eccentric drive for this rotational vibrator is mounted on a bearing and requires a rotation inhibitor coupling to be used.
This type of device is not always satisfactory in that the drive mechanism is more complex than is needed and also the test tubes must be quite securely and yet flexibly mounted so as to permit their movement without slipping out of the drive mechanism.
Vortex mixing is desirable in most automated chemical analyzers, as stated above, and can become necessary when solid supports such as glass beads or magnetic particles are used. Such particles often have a tendency to sink to the bottom of the reaction vessel. For example, in heterogeneous immunoassays, magnetic particles can be used as a basis for separation of the reagents from ligand-antibody bound particles. A particularly desirable particle for such use is the chromium dioxide particle which is disclosed in U.S. Pat. No. 4,661,408 (Lau et al.). These particles have a tendency to settle at a rate which can result in non-uniform sample or reagent mixture. It is therefore desirable that the reagents and/or reaction mixtures be mixed regularly prior to reagent withdrawal.